A conventional automatic assembling apparatus, for instance, an automatic assembling line for assembling such parts as an engine, a suspension, wheels, etc. onto a car body, has an assembling zone in which the engine, the suspension, etc. are coupled to the car body. In the assembling zone, the car body which is supplied by a ceiling conveyor (or work conveyor) is transferred from the ceiling conveyor to a separate conveyor and is positioned thereon, and the engine, the suspension, etc. are raised by a lifter with respect to the car body which has been positioned as above and is held stationary. Thus, the engine, the suspension, etc. are coupled to prescribed positions of the car body. The car body with the engine, the suspension, etc. coupled thereto is then conveyed by the separate conveyor to a thread fastening zone. In the thread fastening zone, a thread fastening operation is done by an automatic thread fastening unit with the car body held stationary again. In this way, the engine, the suspension, etc. are assembled onto the car body. The car body with the engine, the suspension, etc. assembled thereon is then conveyed by the separate conveyor to a back-up zone in which repair with respect to defective thread fastening, etc. is made.
The car body, to which the engine, the suspension, etc. have been secured reliably in the above way, is then returned to the ceiling conveyor to be conveyed to the next step.